How Much Water Do You Need?

Daily water needs scale with body weight — roughly 33 ml per kilogram — then rise with physical activity and heat. This daily hydration calculator starts from your weight, applies an activity multiplier, adds fluid for exercise, and accounts for climate, producing a personalized target in liters, milliliters, and cups.

The Formula

Baseline = Weight (kg) × 33 ml × Activity multiplier. Exercise addition ≈ 350 ml per 30 minutes. Climate addition = 10% (hot & humid) or 15% (hot & dry) of baseline. The target includes water from beverages and food — food contributes roughly 20% of daily intake.

Signs of Dehydration

Thirst is a late signal. Check urine color — pale straw is ideal, dark yellow signals dehydration. Headache, fatigue, dry mouth, and reduced concentration all appear with even 1–2% body-water loss. Sip steadily through the day rather than chugging large volumes at once.